1. Field of the Invention
The present invention relates to a printer for printing on cutforms, for example. More particularly, the invention relates to an automatic cutting device using a worm gear in a power transmission mechanism for transmitting a drive force by a motor to a movable blade.
2. Related Art
In a conventional automatic cutting device of this type, a combination of spur gears is used for reducing the number of revolutions of a drive motor in a power transmission mechanism for transmitting a blade drive force to a movable blade.
A recent technical and market of the automatic cutting device trends to device-size reduction and simplification of the power transmission mechanism. The trend pressurizes designers to employ the worm gear for a remarkable motor speed reduction purpose in the power transmission mechanism of the automatic cutting device.
The prior automatic cutting device using the worm gear, i.e., the combination of a worm and a worm wheel, suffers from the following problem.
Sometimes a foreign matter, e.g., a clip, drops on a moving path of the movable blade, and it stops the blade. When the blade is stopped, an inertia of the power transmission mechanism acts to urge the worm so as to move in the axial direction thereof, and the worm wheel is urged so as to be pressed against the peripheral outer surface of the rotary shaft thereof since the rotation axes of the worm and the worm wheel are perpendicular to each other. Further, the worm and the worm wheel are both moved by the rotation drive force by the motor in the same direction as by the inertia.
Therefore, the worm is pressed against a contact part of the frame where it supports the rotary shaft of the worm by a large force, and its rotation is stopped. That is, the worm is locked.
In the locked state of the worm, the rotation of the motor in one direction is impeded by the foreignmatter, while its rotation in the other direction is impeded by a frictional force generated between the worm and the frame contact part when the worm is pressed against the contact part. In this condition, therefore, it is impossible to remove the locked state by the utilization of the motor. A technique to remove the foreign matter is disclosed in Japanese Patent Laid-Open Publication No. Hei-5-337877. The technique turns the worm shaft by use of a proper tool or turns an added, rotatable gear by the finger to thereby retract the movable blade.
Thus, the manual work to return the movable blade to its home position is inevitable in the prior device. The handling of the automatic cutting device is poor.